This invention relates to pneumatic tires. This invention more specifically relates to pneumatic tires employing small amounts of low density, resilient, polymeric fibers within said tires' internal inflation chamber to permit operation of the tire for a limited time after being punctured.
In a conventional pneumatic tire, when a puncture occurs, a seal or "slow-leak" will usually result as long as the puncturing object remains in the tire. However, the puncturing object will not always remain in the tire. It is common for the puncturing object, usually a nail, to develop some movement as it strikes the road surface. This relative movement results in the puncture hole becoming larger and then the puncturing object will be thrown from the tire at highway speeds. When the puncturing object is extracted from the tire, the normal result is a rapid air loss. This rapid air loss can result in the loss of vehicle control by the driver.
For vehicle safety and motorist convenience, a pneumatic tire has historically been sought which has a means of retarding its deflation upon being punctured. Such a tire would reduce the frequency of tire changes on our high speed interstate highways, thereby resulting in increased safety for the motoring public. Because attention to vehicle safety is on the increase, many vehicle and tire manufacturers have become interested in equipping vehicles with pneumatic tires having the capability of a reduced rate of inflation loss after puncture. Some vehicle and tire manufacturers have become interested in equipping vehicles with such a tire in conjunction with a loss pressure warning device that would inform the motorist when the tire inflation pressure drops below a prescribed amount and then the "slow-leak" feature of such a tire would allow the motorist to take corrective action.
Various approaches to achieve a "slow-leak" pneumatic tire have been proposed without significant commercial success. Fluid puncture sealants which would flow into the puncture hole and either seal or partially seal the puncture hole have been somewhat unsuccessful because they tend to cause the tire to become out of balance. Because of the higher specific gravity of the fluid puncture sealants, if an amount sufficient to substantially restrict the flow of inflation gas through the puncture hole is added to the inside of the tire, then there is sufficient added weight to cause tire balance problems. Another known problem of the fluid sealants is that when the tire is turning at higher speeds, the fluid is concentrated under the center portion of the tread by centrifugal force and will not flow to a puncture hole in the outside contact regions of the tread commonly referred to as the shoulder region of the tread.
Another approach to achieve a "slow-leak" tire that has been proposed is to attach a layer of partially vulcanized elastomer on the inside of the tire, under the tread area, such that when the puncturing object is removed from the tire a small amount of the partially vulcanized elastomer will be pulled into the puncture hole. This partially vulcanized elastomer approach has not had significant commercial success because of manufacturing, technical, and enconomic problems associated with producing such a tire.